A lot of factors come into play. Titan doesn't have a molten iron core or a magnetosphere.

However neither does Venus, and it still retains it's atmosphere, and it's significantly closer to the sun than Titan. That's because Venus has what's known as an inducted magnetosphere. This is due to complex magnetic reactions between the solar wind and Venus's ionosphere.
Someone more qualified can explain this in more detail than I can.

u/quintus_horatius pointed out that Titan is protected by Saturn's magnetosphere, which is actually only party true. Titan's orbit actually enters and exits Saturn's magnetosphere, so part of it's orbit is protected and part isn't. As a result Titan is actually losing atmosphere due to the interactions between Saturn's magnetosphere and Titan's ionosphere. It's not currently known to be a significant loss, but it's a large area of study that is still being investigated.

Also Saturn and Titan lie further from the sun than us, so there is significantly less solar wind. They also lie in an extremely cold region of space. It's cold enough to freeze methane remember. As a result the energy that the already reduced amount of solar wind distributes into Titan's atmosphere is lost at a much faster rate. You're effectively significantly reducing the amount of speed and energy the particles have to escape Titan's gravitational pull. (Imagine a rocket trying to reach escape velocity at 10% thrust.)

At this point i'll invite someone much smarter and more qualified than I am to explain these things further, that's the limit of my knowledge on the subject! Hope it helped!

I have a question regarding something you said! Imagine a rocket trying to leave the atmosphere with 10% thrust. What would happen? If they have the same amount of fuel would it just take longer or would they not be able to go fast enough to escape gravity?

From a very simple analysis, if the engines have equal efficiency, you're going to need much more fuel to reach orbit at lower thrust. This is because you will need to overcome the effects of gravity and air friction for a longer amount of time. Since needing to carry more fuel means more mass, and thus less acceleration per unit fuel, more and more fuel is needed to reach orbit.

This can be seen using the generalized Rocket Equation. Unfortunately the simpler Tsiolkovsky Rocket Equation can't be used here, since it assumes the force of gravity to be zero. As long as you're accelerating pretty quickly (like a rocket), this is generally not a big deal, since the amount of power used overcoming gravity is small for such a short time period - most of your fuel is spent increasing your kinetic energy. If on the other hand, you spend more time accelerating (as you would with lower thrust), the acceleration of gravity is no longer negligible - you spend more time, and thus more fuel, fighting the gravitational field.

This is why rockets try to accelerate to escape velocity (using high thrust). Less fuel is required to reach escape velocity and then just let the rocket go, than is needed to try to leave the Earth at a lower velocity, which would require a prohibitively longer thrust.

Just consider if you built a rocket that produces just enough thrust to hover above the ground. It takes a certain amount of power, and thus fuel, to hold you there for a given amount of time. The longer you spend reaching orbit, the larger the proportion of your fuel you're spending simply overcoming the force of gravity, and lower the proportion you're using to actually increase your altitude.

If you're in a vacuum and not subject to large gravitational forces, then I would say that it would just take longer to accelerate to a given velocity with lower thrust.

You don't actually need to reach escape velocity to get up to a certain altitude. If you move away from the earth at 1m/s, eventually you will escape Earth's gravity well and no longer be pulled back into it.

That is, once you reach the distance from Earth where the escape velocity is 1m/s, you could turn off your thrusters, and never come back to Earth.

Escape velocity just refers to the initial velocity you need to have, with no additional thrust, to escape from Earth's gravitational pull, starting from the Earth's surface. If you have a source of thrust, the concept of escape velocity doesn't really affect you (other than that once you reach the escape velocity for your altitude, you can turn off your thrust).

You don't actually need to reach escape velocity to get up to a certain altitude. If you move away from the earth at 1m/s, eventually you will escape Earth's gravity well and no longer be pulled back into it.

Yes, but that's not very efficient. And that's not how rocket launches are typically done.

The initial reference to air friction was a red herring. The reason you want to get into orbit as fast as quickly as possible is because you'll be wasting less time fighting gravity, which is a much more significant problem to overcome, especially because atmosphere thins out very quickly compared to the gravitational force that needs to be overcome.

It's quite difficult to calculate actually. As you said, air friction depends on velocity, so if you reach orbit by moving away from the Earth at low velocity, yes, the amount of fuel per second you were using to counteract the force of air friction would be lower. Of course, you would spend much more time working against that force.... and the force of air friction falls rapidly as you gain altitude...

So the amount of fuel spent counteracting air friction is dependent on time of flight, time spent in different portions of the atmosphere, and velocity (and other things I'm sure). So it's not as simple as saying "getting to a certain altitude at lower velocity means you spend less energy fighting air friction".

With regard to air friction, my understanding is that the force is equivalent to the square of velocity. The time to cover a distance is inversely proportional to velocity. Thus, the energy required to overcome air friction over a given distance is proportional to the velocity.

Now--I understand rocket science is complicated. While air friction consumes less fuel/distance at lower velocities, and the atmosphere is denser and increases air friction at lower altitudes. Nonetheless, the less time a rocket spends overcoming gravity the better, and this is a massive factor, as is the simple fact that burning fuel quickly (and increasing thrust, and therefore velocity) lightens the rocket, decreasing the impact of gravity and increasing acceleration.

There's quite a bit of calculus there, but the rough formula goes: increase acceleration as quickly as possible to 4g, if you have humans in your payload...

The latter, assuming the rocket resembles those we currently use. For instance, a fully-loaded Saturn 5 weighed in at 6.2 million lbs. Its engines could provide 7.65 million lbs of thrust. As you can see, if the engines could have been throttled back to 10% (not currently possible for most engine types, but that's another discussion) they would provide 0.7 million lbs of force to a 6.2 million lb rocket - not enough to lift it off the pad. It wouldn't matter how long you ran the rocket for, it wouldn't be going anywhere.

This is of course not the case if you are in space, or orbit, or anywhere except trying to leave the ground. In truly empty space, it wouldn't matter what percentage you ran the rockets at, assuming a uniform efficiency (the rocket is as efficient at 10% as 100%; again seldom true) when the fuel was gone you'd be going at the same velocity. Even out in the solar system though, there is gravity that is often significant to interstellar probes - and the specifics of the result can get quite complicated, especially if you use fuel-saving tricks like slingshot maneuvers.

it probably wouldn't be able to leave the ground, let alone the atmosphere, at only 10% thrust. not only does the rocket have to accelerate itself continuously, but it also has to fight air resistance and gravity.

so gravity is a constant, therefore it will take a constant amount of energy just to resist gravity alone (Force=mass*gravity).

Air resistance is a bit different, it is not a constant and it is dependent on velocity. the faster the rocket is going, the more drag it creates. but it isnt quite that simple of a relationship. as the speed increases (linearly), the power it takes to overcome the air resistance is cubed. For every time you double your speed, the air resistance is Quadrupled. so very early on, the air resistance wouldn't amount to a large percentage of the output but you can see how the energy to overcome this could add up very quickly at higher speeds.

so you have gravity and air resistance. for the most part (I'm simplifying this quite a bit here, there are a ton of other considerations that go into rocket science) these are the only things holding you down. the rest of the energy the rocket outputs goes toward accelerating the rocket upwards.

now, at 10% thrust a rocket might be able to lift off the ground and start accelerating upwards. And even if it is able to lift off, pretty soon it will reach a velocity where the forces of Air Resistance + Gravity will equal the amount of power output from the rocket. when it reaches this point, it would stop accelerating and maintain a constant velocity.

when you're stuck at a constant velocity, your hopes for leaving the atmosphere go down pretty quickly. because you are still burning a constant amount of fuel fighting gravity and a constant amount of air resistance, but your time spend enduring these forces has increased tremendously, and you simply cant hold enough fuel to sustain that output for such a long duration of time.

There is a significant amount of both methane and ethane in the atmosphere of Titan, and in fact oceans on the surface, that are produced by outgassing of volatile material. And while molten 'rock' may not flow on the surface, there may be evidence of liquid water volcanism. In the temperatures at the surface of Titan, water ice acts more like a rock in the way it deforms. So it's definitely not traditional, but the large amount of methane is a definite tell of cryovolcanism, yes.

'Cold' doesnt work that way, in order to estimate how much something cools have too look at the thermal contact, and there is none here. The solar wind exists with some energy per particle and arrives with similar energy, 1.5KeV electrons ~0.07c~2⋅104 km/s, 10KeV protons ~4⋅10-3 c ~1.4⋅103 km/s, in comparison the suns escape velocity is ~617.5 km/s, i guess that is apparently a large fraction of the speed for the protons. Of course, they wont have lost all of it when they reach saturn.(and they'd already have lost energy reaching mars, earth etc. too, actually wp is unclear on when they have that energy, at the sun surface?)

The distance is also significant; 9AU, so ~80 times less light than on Earth, ~28 times less than mars..

Mart's point about cold wasn't that the solar wind itself would cool. Rather that the components of the atmosphere would have less kinetic energy. Thus they would require a stronger solar wind to get knocked out.

The amount of solar radiation Titan receives is subject, just like anything else away from a light and heat source, to the Inverse Square law. Others have mentioned it in passing, but I thought I would plug in some numbers so we know what we're dealing with here.

Jupiter, for example, is 5 times more distant than Earth from the Sun, so it gets only a 25th (5 squared = 25), or 4%, the solar energy that we get.

And Saturn is 9 A.U from the Sun, so it gets a mere 1/81 the solar activity (less than 1¼%).

Are you sure that Venus doesn't have a molten core? Other sources on the interwebs are never completely reliable, but from what I'm seeing- it looks like Venus has a partially molten core- is that enough to add some magnetic resistance?

Also, can you, or someone explain the inducted magnetosphere in more detail?

Beyond the explanations given so far, remember that Titan is very cold, nearly -300°F. Many of the elements that would be gases on Earth are liquid or solid on Titan.

Titan's atmosphere is much heavier ... in fact, it is 7 times more massive than our atmosphere. It is mostly nitrogen, with some methane and a few trace gases. So, even though Titan itself is much less massive than the Earth, the atmosphere still presses down with a much greater force than our atmosphere.

Given that Saturn is 9 times farther from the Sun than the Earth and since the effect of the solar wind dissipates in proportion to the square of the distance, the solar wind would have about 1.2% of the effect on Titan that it does on the Earth.

Given these figures, what would a human have to be wearing or living in to survive these temps? Do we have a current day tech that would allow humans to survive on Titan? Genuine question not a sci fi thing.

Humans could live in a sealed container, like the ISS except on the ground, and we could get out and about in suits like we did on the moon.

I'm sure that, as long as we don't screw things up too much here on Earth, humans will eventually make it to Titan. It's a neat place. But don't look for a trip like that any time soon. It could us take us hundreds of years to get there in person, and we probably wouldn't want to stay very long. Maybe in your lifetime you will see a robot explorer that moves around and does science, but, unless those robots find something we really, really need back on Earth, the reasons for going to Titan are not much different than the reasons for going to Mars or the Moon.

There's a fundamental difference. On the moon there is no atmosphere, so heat can only be lost by thermal radiation. On Titan you will also lose heat by convection/conduction. You would need significantly better isolation and/or a much stronger internal heat source in a space suit or space base built for Titan compared to what is needed in orbit or on the moon. It's probably possible but it would waste a lot of energy and be bulkier to move around in.

I'm not sure what that guy meant but Titan's surface pressure is 1.45 times Earth's. I don't think think the pressure would be an issue, but airtight suits would probably be most practical anyway because of the cold.

Divers regularly dive down to an excess of 10 atm with special helium-mixed compounds for breathing; however, the pressure would have to be changed slowly from 1 atmosphere if people were to go there. A compression/decompression chamber would be needed if one area was at earth pressure and one at titan's pressure.

That would definitely be possible- however, it would be more difficult as the spacecraft would have to be built to withstand seven times the pressure as normal. Perhaps the descent capsule could be built stronger or something like that.

Actually, even that wouldn't be nessecary assuming you didn't reduce pressures in a hurry. Nitrogen would dissolve in tissues sure, but as long as the pressure doesn't reduce, the nitrogen won't boil out of your blood. The only thing to watch out for would be oxygen toxisity. At roughly 8 atm oxygen will actually become toxic to the body, causing you to cough. Divers can die from this because they can't keep their regulator in their mouth.

Good point, I personally don't have issues with nitrogen narcosis, but it is a common problem. From what I understand it tends to be person specific and based on the military dive tables it seems that physical fitness may have an influence.

Personally, I hit oxygen toxisity before getting narc'ed. Still, a helium blend in the air would solve all of these problems.

The pressure on the surface of Titan is about 1.5 times the pressure here on Earth. That pressure is fine without any sort of pressurized space suit, and the atmosphere doesn't contain any substances that are toxic.

The temperature, however, is about -180 degC on Titan. That's 90 degC colder than the coldest temperature recorded on Antarctica. You'd need really good insulation to keep warm in that environment.

Essentially you would need an air tank for breathing and really good insulation.

Just wanted to clarify a few things: You're referring to the Inverse Square Law, correct?
And although Titan's atmosphere is 7 times heavier, isn't the atmospheric pressure at the surface only 1.5 times as strong?

The inverse square law applies to distance. Mass works directly. The force of gravity between two bodies is proportional to the combined mass of the bodies, divided by the square of the distance between them: g = (m1+m2)/d2 (x the gravitational constant...)

Titan's atmosphere is much heavier ... in fact, it is 7 times more massive than our atmosphere. It is mostly nitrogen, with some methane and a few trace gases. So, even though Titan itself is much less massive than the Earth, the atmosphere still presses down with a much greater force than our atmosphere.

First of all, what do you mean by "7 times more massive than our atmosphere"? Are your referring to density? Or are you saying that total mass of all the free gas molecules on Titan is 7 times that of the same measurement on the Earth? Either way, it doesn't even matter. The ability to retain an atmosphere is related to two things -- the escape velocity (which is derived from the mass of the planet and the radius of the outer edge of the atmosphere) and the temperature of the gas. The hotter the temperature of the gas, the faster its individual molecules move, to the point where every so often one of them will randomly get hit and end up moving so fast away from the planet that it escapes.

What keeps Titan's atmosphere, then, is the very low temperature of Titan, which is caused by the vastly reduced solar flux at Saturn's orbital radius as compared to our own. The total mass of the atmosphere has nothing to do with it, unless the atmosphere is so massive that it's actually contributing significant gravitational force to raise the escape velocity (this occurs with gas giants, which are primarily composed of gas, but not rocky planets).

It is mostly nitrogen, with some methane and a few trace gases.

The Earth's atmosphere is mostly nitrogen too.

So, even though Titan itself is much less massive than the Earth, the atmosphere still presses down with a much greater force than our atmosphere.

Yes, the atmospheric pressure at the surface will be higher. But that doesn't have anything to do with loss of atmosphere molecules, which occurs at the very top of the atmosphere, where pressure is necessarily nearing exactly zero.

EDIT: I forgot one critical factor that determines whether an atmosphere can escape -- the mass of the molecules that make up the gas themselves. Hydrogen atoms are much lighter than, say, molecules of carbon dioxide, so in a gas of a given temperature, the hydrogen atoms can be accelerated a lot faster since they have much less inertia, and thus the hydrogen will escape from the atmosphere at a much higher rate than other elements in the gas. Thus why the Earth's (and Titan's) atmospheres are mostly nitrogen, even though hydrogen and helium are much more common ingredients in the universe at large; neither of these celestial bodies have sufficiently high escape velocities to retain them for long periods of time (unlike, say, Jupiter and Saturn, which do, and are thus composed primarily of them).

Yes, and while Titan's atmosphere is much more extended than the Earth's, the energy of the solar wind is greatly diminished.

Just like I am sure that gases escape Earth's atmosphere into space, such as Helium, I am sure that Titan loses some atmosphere to the solar wind. However, I believe that as long as a planet generates more gas at the surface than it loses, it will continue to hold its atmosphere.

Venus seems very unprotected compared to the Earth, yet its atmosphere is much denser. In the distant past, Venus liberated a great deal of gas at the surface from heat and volcanoes. While it is volcanically active, and probably has more volcanoes than any planet on the solar system, it's not very active now, if at all. But it still has more than 1,600 volcanoes. The gases that remain on Venus are relatively heavy, as the lightest gases all escaped into space long ago. While the solar wind strips the upper atmosphere of gases continuously, the atmosphere is so dense that the solar wind would have little if any effect further down in the atmosphere.

Obviously every planetary body that currently has an atmosphere is either liberating more atmosphere at the surface than it is losing to the solar wind, or the rate of loss is low enough that it would take billions of years for the solar wind to have a significant effect.

Earth's atmosphere is protected by the magnetosphere, so gas losses into space are minimized. Because of plate tectonics, the Earth is liberating new gases into the atmosphere continuously, although the planet has cooled enough that the rate of that liberation of gases is lower than it was earlier in the planet's history.

Venus has a very weak magnetosphere, but was hot enough to liberate a thick atmosphere, and a runaway greenhouse effect keeps it very hot. The light gases were lost into space long ago, but the lack of a carbon cycle enabled CO2 to build up. Now the atmosphere is more than 90 times denser than the atmosphere on Earth.

Titan gets some protection from Saturn's magnetosphere, but many elements that would be gaseous on Earth are liquids or solids on Titan. The solar wind is much weaker at Titan than at the Earth, so its effect is minimal. Titan also has cold volcanoes that liberate additional water and methane into the atmosphere.

A planet gets to retain its atmosphere:

if the rate of the loss of that atmosphere is less than the rate that atmosphere is increasing,

if those rates are at equilibrium, or

if the net loss of the atmosphere is so small that it takes billions of years for the atmosphere to completely erode.

Saturns own magnetic field is large enough to encompass and "protect" Titan from solar winds and other large radioactive events that occur in space.

As for this:
"Many of the elements that would be gases on Earth are liquid or solid on Titan."

This is just a theory. We don't know for sure if Titan has liquid methane. It does seem likely, however that is also based on another theory about a meteorite impacting Titan millions of years ago and bringing methane that way (since methane is a by-product of the metabolism of organisms.)

Not that odd if you think about it. If you have a wet shirt, the water evaporates faster if you put it in the wind. The same principle applies on a planetary scale with the solar wind.
If the planet (or shirt) had nothing to blow away then that stream of matter would add mass, albeit a relatively tiny amount compared to the overall mass of the object. It is not that the wind doesn't add mass, it is just that it is stripping away more than can be retained by the object.

Perhaps the misconception i had was due to the ratio of the cross section of the planet , essentially the straight on approach, versus the cross section of the atmosphere (viewed as a thin ring only). But this ratio which tends toward being very large in favor of the planet, and thus those solar wind particles that get absorbed into the atmosphere, is completely incorrect due to the tenuous nature of the thinnest and farthest out reaches of the atmosphere, which in turn sends the atmosphere's cross sectional area into the stratosphere.

All of this potential misconception is perhaps why one such as myself would get confused about the reduction of atmospheres over time.

If you could successfully terraform Mars, the loss of atmosphere to the solar wind would occur in geologic timescales, not human ones. You could "top off" the atmosphere regularly to keep it habitable. Furthermore, "habitable" wouldn't mean the same atmospheric pressure as Earth. The artificial atmosphere on the space station is much thinner than Earths. This makes the task of maintaining an atmosphere on Mars easy.

As some people have pointed out, the relatively cold region of space Titan occupies may have something to do with it. The temperature in Titan's area allows for a greater variety of compounds to make up the atmosphere. Also, the solar wind is not nearly as much a factor for Titan as it is for Mars.

Nonetheless, we don't really know why Titan has an atmosphere. Moons of similar size don't, and, as you noted, it doesn't have a liquid core. Although, what may be going on is that Titan's atmosphere is being continually replenished by the decomposition of compounds in its interior.

well, the reason why there is no hydrogen in our atmosphere is that at earth temperatures, each hydrogen molecule is likely to have terminal velocity, so all the hydrogen molecules have since left. Meanwhile heavier elements are extremely unlikely to achieve escape velocity, so they are still here. As far as the moon goes, every element is likely to have escape velocity, as the moon is subject to the same energy from the sun. Outer moons are subject to far less energy from the sun, so the molecules are moving slower, and are unlikely to achieve escape velocity and thus stay bound.

"The inner core is solid, the outer core is liquid. The mantle is solid >but malleable (not brittle, think caramel vs hard candy) and can flow on geologic timescales. Only small pockets of the mantle are molten. If melt rises to the surface or near surface then you get volcanic activity."

The inner core is solid, the outer core is liquid. The mantle is solid but malleable (not brittle, think caramel vs hard candy) and can flow on geologic timescales. Only small pockets of the mantle are molten. If melt rises to the surface or near surface then you get volcanic activity.